The present invention pertains to tertiary oil recovery processing and, more particularly, to improving the efficiency of heater treaters used in moisture removal for heavy oil.
Presently, new oil wells are being drilled in remote areas and to greater depths. As such, new wells are becoming very expensive and the possibility of reworking old oil wells is increasingly attractive.
In the past, oil wells were drilled and when natural pressure ceased forcing oil out of formations, the well was considered as nonproducing. In eariler wells, natural pressure diminished quickly since the majority of these wells were shallow.
In most oil wells that are being reworked, the oil remaining is extremely heavy, having a density much closer to water than the oil originally produced. As a result, this oil may be suspended in water to the point where oil constitutes only thirty percent (30% ) of the solution. A good portion of this water is freewater and may be separated from an oil-water emulsion very easily by settling.
The process for heavy oil recovery is fairly simple and well known in the prior art; however, for the sake of clarity, a brief outline will be presented.
Heavy oil is forced from subsurface formations by the use of high pressure steam injection or by any one of many secondary or tertiary oil recovery methods currently in use in the art. In general, the heavy oil arrives at the surface in a slurry at approximately one hundred forty degrees Fahrenheit (140.degree. F.). This slurry may be greater than seventy percent (70%) water, primarily from ground water, although steam injection does add slightly to the water content, although most subsurface oil is significantly less dense than water and easily separates from the subsurface water. However, heavy oil of the type obtained in secondary or tertiary recovery has a density much closer to that of water and is more difficult to separate.
As a result, chemical emulsion breakers, such as surfactants, are added to the water/oil mixture and the mixture is placed in a settling tank, sometimes referred to as the freewater knockout tank, for several hours. When the freewater has had an opportunity to settle, a water/oil emulsion along with the chemical coalescers are drawn off the top of the settling tank. Water is drained from the bottom of the tank.
The water/oil emulsion is piped to a heater treater where the emulsion is heated from approximately one hundred to one hundred fifty degrees (100.degree.-150.degree.) to between two hundred and two hundred fifty degrees Fahrenheit (200.degree.-250.degree. F.). The emulsion has been reduced from approximately seventy percent (70%) water as it arrives from subsurface formations to approximately thirty-five percent (35%) water from the freewater knockout tank. After the emulsion is removed from the heater treater, water constitutes only about three percent (3%) which is acceptable for transport to a facility for further refining.
The preshipment process comprising the freewater knockout tank along with the chemical surfactants and the heater treater add significant costs to the secondary and tertiary recovery of heavy oil.